Embryology Flashcards
Where does the allantois originate from?
Evagination of the secondary yolksac (future hindgut) endoderm. Will stick out into the extraembryonic (somatopleuric) mesoderm alongside the umbilical arteries and umbilical vein, since the connecting stalk forms the vessels which communicate with the placenta.
What does the allantois give rise to in the fetus? What does it communicate with?
The distal part (away from the cloaca, communicating with the connecting stalk / umbilical cord ) should involute into a fibrous band.
The remainder of the allantois forms the urachus (which communicates with the umbilicus and also involutes into a fibrous band). the urogenital sinus, and the urethra.
It communicates with the hindgut structures of the urogenital sinus, which will form the bladder and the urethra.
What will patent urachus present with?
Communication between bladder and umbilicus via urachus -> urine leakage from the umbilicus
What give rise to the median and medial umbilical ligaments?
MediaN = allaNtois
MediaL = umbilicaL arteries (paired)
What causes congenital umbilical hernia?
Incomplete closure of umbilical ring, due to defect in linea alba.
Reducible, asymptomatic, benign, and self-resolving. Usually minimal inclusion of abdominal contents.
How do you tell a vitelline fistula apart from a patent urachus?
Vitelline fistula will show meconium draining thru the umbilical ring.
Remember, vitelline fistula is due to Meckel’s diverticulum persisting and communicating with umbilicus. It, along with the urachus, normally communicates with the umbilicus. However it is present due to the vitelline duct, which connects the MIDGUT to the yolksac.
What goes wrong in a PAX6 mutation?
6543
Eye development is controlled by the PAX6 gene.
Mutation of PAX6 gene -> congenital aniridia
What is the most important transcription factor in guiding the segmental organization of the embryo?
Hox (Homeobox) genes
-> if you aren’t sure of a transcription factor, guess this.
What area of the embryo releases Sonic Hedgehog? What does it do?
Zone of polarizing activity - controls development of anteroposterior axis of the limbs
Also controls CNS development -> deficiency leads to holoprosencephaly (as in Patau syndrome)
What two growth factors are released at the end of the limb, and what is this limb end called?
Apical epidermal ridge - releases FGF and Wnt-7
What do FGF and Wnt-7 control?
FGF - controls elongation on the proximal-distal axis
Wnt-7 - controls the only axis we haven’t mentioned so far -> dorsal-ventral
What is the morula?
The compacted embryo, in stages after the third cleavage (8-cell stage). Blastomeres (individual cells) adhere tightly to eachother and cell divisions between blastomeres are no longer visible (squished together)
When does the morula turn into a blastocyst?
Via cavitation -> formation of a cystic cavity, the blastocoel.
Cavity has trophoectoderm on the outside and an inner cell mass
When does implantation occur?
Between days 6-8, this is when the trophoectoderm differentiates into syncytiotrophoblasts and begins secreting hCG
What is the definition of gastrulation?
The formation of the trilaminar embryo
How is the extraembryonic coelom formed?
Small lacunae appear in the extraembryonic mesoderm (between Heuser’s membrane which lines the primary yolk sac, and the trophooblast layer) and coalesce. Within 24 hours, this chorionic cavity is formed.
What are the two layers of the extraembryonic mesoderm after the chorionic cavity is formed?
- Splanchnopleuric mesoderm - lines the primary yolk sac
2. Somatopleuric mesoderm - lines the cytotrophoblast and continues around amniotic cavity
What forms the secondary / definitive yolk sac?
Cavity lined by migrating extraembryonic endoderm, it is much smaller than primary yolk sac.
-> While the chorionic cavity is forming, a second wave of hypoblast cells proliferates and displaces the Heuser’s membrane lining the primary yolk sac. These hypoblast cells which line the splanchnopleuric mesoderm become the extraembryonic endoderm, forming the yolk sac. The cells which are displaced are the primary yolk sac, which turns into cysts and are displaced to the opposite side of the embryo.
What is the function of the connecting stalk?
It is a mass of extraembryonic mesoderm which connects the embryo to the chorionic plate, since the chorionic cavity is getting much larger.
What is the chorionic plate?
Also called chorion, it is the wall of the chorionic cavity. It is somatopleuric mesoderm + cytotrophoblast + syncytiotrophoblast
What is the role of the secondary (definitive) yolk sac in humans?
Transfer nutrients in weeks 2 and 3 before the uteroplacental circulation is established. Hemopoesis first occurs in the vascularized extraembryonic splanchnopleuric mesoderm until week 6 it starts in liver. Will also give rise to primordial germ cells in endodermal layer.
What are the three stages of transformation of the chorionic stem villi?
- primary - columns of cytotrophoblast surrounded by syncytiotrophobolast
- secondary - extraembyronic somatopleuric mesoderm invades to form core
- tertiary - mesenchymal cells in the extraembryonic somatopleuric mesoderm differentiate into capillaries and blood cells
What are the caudal and cranial ends where the ectoderm and endoderm adhere?
Cranial: Buccopharyngeal
Caudal: Cloacal membrane
What is the allantois?
Structure forming from outpouching of extraembryonic endoderm from caudal wall of definitive yolk sac into the connecting stalk. It will be incorporated into the umbilical cord later, and is rudimentary in humans
What is the neurenteric canal?
Transient connection from yolk sac to amniotic cavity as a result of formation of notochordal plate (Arises from lumen of notochord canal)
What is the neural plate? Where is it?
Neural ectoderm forms this structure. It is more cranial since the notocordal process ends at the prechordal plate and runs mostly cranial
This is the area of ectoderm between the prechordal plate and the primitive node (where the notochord is)
Where is the paraxial mesoderm segmented vs unsegmented?
Unsegmented when it is rostral (cranial) to otic vesicles, will become head mesoderm
Segmented when it is caudal to the otic vesicles, which will form somites on both sides of the developing neural tube
What are somites? Which components are dorsal and which ones are ventral?
Somites are condensations of mesenchymal cells on both sides of the neural tube. They develop from segmented PARAXIAL mesoderm.
Dorsal: Myotome, dermatome, lateral somite
Ventral: Sclerotome
What is the function of the sclerotome?
Dorsal element of the somite, it loses its compact organization first and migrates towards developing notochord and neural tube to form vertebral column later in development.
What is the function of the lateral somite?
Migrates to final destinations and gives rise to all voluntary striated muscles of body wall and limbs (hypaxial muscles)
What is the dermomyotome?
Two segments of the dorsal somite which fuse and give rise to different but related things
Dermatome - gives rise to DERMIS of skin over dorsal region of trunk
Myotome - gives rise to segmented muscles of axial skeleton (epaxial). I.e. intrinsic muscles of the back and ribs associated with spinal cord
What does the intermediate mesoderm give rise to?
It is unsegmented. Gives rise to:
Connective tissue and smooth muscle of gonads, urinary system, reproductive tracts
-> gonadal ridge
What forms the intraembryonic coelom? and what two layers does it create?
Lacunae form within the lateral (plate) mesoderm, which coalesce and form a continuous cavity. Forms two new layers of mesoderm: Somatic (parietal) and splanchnic (visceral)
How do the extraembryonic and intraembryonic coelom’s meet?
Whenever the somatopleure and splanchnopleure split at the edges of the intraembryonic coelom, breaking the lateral mesoderm apart. This opens the coelom.
Lateral mesoderm at this point forms the somatic (parietal) and splanchnic (visceral) mesoderm
What does the somatic (parietal) mesoderm give rise to?
Skeleton of the limbs, connective tissues of limbs and trunk, dermis of ventral body wall and limbs, connective tissues of external genitalia, smooth muscle and connective tissues of the blood vessels
What does the splanchnic (visceral) mesoderm give rise to?
mesoderm give rise to?
Smooth muscle and CT of GI tract, associated glands, and abdominal mesenteries. Smooth muscle and CT of respiratory tract and associated glands, cardiac muscle and the smooth muscle and connective tissue of their blood vessels.
What is the septum transversum?
It is the most cranially located mesoderm, cranial to the buccopharyngeal membrane as well as the cardiac mesoderm, and is adjacent to the extraembryonic mesoderm. It is a mesenchymal cell mass
What is the fate of the septum transversum?
Becomes the majority of the mesenchyme of the developing liver, and will also give rise to epicardium, central portions of diaphragm, and esophageal mesentery. (It is located outside the buccopharyngeal membrane)
What is the rhombencephalon and its two secondary subdivisions? What do they give rise to?
Hindbrain brain vesicle
- Metencephalon - pons and cerebellum
- Myelencephalon - medulla and spinal cord
What do neural crest cells in the trunk region become?
Dorsal route: leads to skin, give rise to the melanocytes of epidermis and hair follicles.
Ventral route: They travel between anterior parts of somites and will form dorsal root ganglia, sympathetic ganglia, parasympathetic ganglia, para-aortic ganglia, Schwann cells, and C-cells of adrenal medulla
What forms the midgut?
The portion of the gut lying between the foregut and hindgut, but still connected to the yolk sac. Forming the midgut pinches off the yolk sac somewhat and forms the vitelline duct
What forms the peritoneal cavity?
The transverse folding brings ends of the somatopleure together, forming the ventral wall of the peritoneal cavity. It is lined with splanchnic mesoderm (around the gut), inside of outer wall is somatic mesoderm, and outside of outer wall is surface ectoderm
Why is the definitive foregut / hindgut different than the definitive midgut?
There is a space where the splanchnopleure and somatopleure cannot fuse because the yolk sac is preserved. The small connecting tube is called the vitelline duct
What structures pass through the umbilical ring?
- Connecting stalk:
Contains: Allantois, and umbilical vessels (two arteries and one vein). - Vitelline duct with vitelline vessels (from primitive hemangiogenesis, connecting to yolk sac)
- Canal connecting peritoneal cavity of fetus to extraembryonic (chorionic) cavity, since the surface ectoderm is unable to fuse when the yolk sac is hanging out
What is the mechanism of toxicity in fetal alcohol syndrome? What is the worst possible outcome?
Failure of cell migration
Heart-lung fistulas with holoprosencephaly can occur in the most severe form
What does fusing of the chorion with twinning tell you?
They are definitely identical twins
Can patients with uterus didelphys have children?
Yes -> double all the Mullerian duct structures due to complete failure of fusion, but pregnancy is possible
What are pharyngeal clefts, arches, and pouches?
Cleft - ectoderm in groove, caudal to corresponding arch
Arches - mesoderm / neural crest between the grooves.
Pouch - outpockets of pharyngeal endoderm that lies close to to cleft in the grooves (making a membrane).
Arch is cranial to the corresponding cleft/pouch membrane
What is the content of the arches of the pharyngeal apparatus?
Mesoderm - muscles, arches of the aorta (i.e. arch 1 of aorta is in the first subdivision, gives rise to the maxillary artery)
Neural crest - gives rise to bones and cartilages of the face
What are the subdivisions of the first pharyngeal arch and what do they outline?
- Maxillary prominence (Cranial)
- Mandibular prominence (Caudal)
Outlines the stomodeum (primitive mouth)
What muscles are formed by arch 1? What innervates them?
Muscles of mastication, mylohyoid, anterior belly of digastric, tensor tympani and tensor palatini
All sensory / motor innervation of arch 1 comes from trigeminal nerve (CNV)
What bones form by endochondral ossification from arch 1? What is the function of the rest of the cartilage?
Malleus and incus only.
Makes sense because tensor tympani is V3-innervated and inserts on malleus.
Rest of mandibular cartilage (e.g. Meckel’s cartilage) just functions transiently to reinforce the developing strucutures
What bones from arch 1 form by intramembranous ossification?
Palatine, maxilla, mandible, zygomatic arch, part of temporal bone
What is the second pharyngeal arch called and what muscles develop from it?
“Hyoid arch”
Muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius (to stapes)
all innervated by Facial nerve (CN7)
What are the skeletal derivatives of the second pharyngeal arch? What type of ossification is it?
Stapes, and all bones associated with stylohyoid muscle, including:
Styloid process of temporal bone, stylohyoid ligament (connects stylohyoid muscle to the lesser horn of the hyoid bone), lesser horn and upper part of body of hyoid bone
All endochondral ossification!
What is the third pharyngeal arch called and what muscle arises from it?
“Glossopharyngeal arch”
Muscle: Stylopharyngeus
Innervation: Glossopharyngeal nerve (CN9)
What skeletal components arise from the third pharyngeal arch, and by what process?
Lower part of body and greater horn of hyoid bone
Endochondral ossification
All but most of arch 1 is EO
-> explains why achondroplasia has large maxilla / mandible
What muscles are derived from the 4th + 6th arches?
Pharyngeal constrictors (innervation: CN10 - pharyngeal and superior laryngeal branches) and intrinsic muscles of the larynx (innervation: CN10 - recurrent laryngeal, minus cricothyroid innervated by external branch of superior laryngeal nerve)
What skeletal components do the 4th + 6th arches give rise to?
Just the laryngeal cartilages - thyroid + cricothyroid
What is the function of the first pharyngeal pouch (endoderm)?
Elongates to form auditory tube, middle ear epithelium, and inner surface of tympanic membrane
What do dorsal and ventral wings of pouches 3 and 4 form?
Pouch 3:
Dorsal - inferior parathyroids
Ventral - Thymus
Pouch 4:
Dorsal - Superior parathyroids
Ventral - Parafollicular (C) cells
What do the first and second aortic arches become?
1st - maxillary artery (since Trigeminal = Arch 1)
2nd - Stapedial artery (since Stapedius = Arch 2)
What does the third aortic arch become?
3rd - common carotid artery / proximal part of internal carotid artery
-> makes sense b/c 3rd arch is glossopharyngeal arch, and CN9 innervates the carotid bodies
What does the 4th aortic arch become on the right and the left?
Remember this is vagus nerve arch
Right 4th - proximal right subclavian artery, where the recurrent laryngeal nerve wraps around
Left 4th - aortic arch (more proximal to where left recurrent laryngeal nerve wraps around)
What does the 6th aortic arch become?
Proximal part of pulmonary arteries on both sides
Ductus arteriosus (extending from proximal pulmonary arteries) -> makes sense because left recurrent laryngeal nerve wraps around just distal to the ligamentum arteriosum
What happens to the lateral lingual swellings?
They increase in size and fuse, to overgrow the tuberculum impar. Since they are derived from arch 1, sensory innervation to anterior 2/3 of tongue is via the lingual branch of CN V.
How do taste buds (fungiform papillae) come to be derived from CN7?
The second pharyngeal arch tissue of the tongue migrates under the tongue as the lateral lingual swellings fuse. Taste buds of anterior 2/3 are provided by chorda tympani (CN7)
What happens to the hypobranchial eminence?
Expands mostly from arch 3, overgrows arch 2, to form posterior 1/3 of tongue.
What separates anterior and posterior tongue?
The sulcus terminalis (between the lateral lingual swellings and the hypobranchial eminence)
What do the alar and basal plate become?
Alar plate - dorsal - becomes sensory
Basal plate - ventral - becomes motor
What gives rise to the posterior pituitary and pineal glands?
Diencephalon, which also gives rise to the thalamus and hypothalamus
What gives rise to the pons and cerebellum?
Metencephalon, the first division of the rhombencephalon
What does the myelencephalon give rise to?
Medulla + spinal cord beginning
What gives rise to the macroglia vs microglia?
Macroglia - neuroectoderm
Microglia (i.e. macrophage-like cells) - mesoderm
Is spina bifida occulta associated with increased serum AFP?
No! Only the spinal arch will be open, but not the subarachnoid space
What are the three stages of kidney development?
- Pronephros - 4th week
- Mesonephros - 4th to 9-10th week
- Metanephros - 5th - maturity
What does the pronephros do and what is its fate? What region of the body is it in?
It induces the underlying mesoderm in the cervical region to segment and form the pronephric ducts, but it never forms a functional nephotome, and completely disappears when the mesonephros starts forming
What is the kidney functioning in the mesonephros stage? How does it degrade?
One pair of excretory tubules will be formed per somite, with an afferent glomerular arteriole arising directly from the dorsal aorta. Forms functional renal corpuscles
Degrades segmentally from cranial to caudal.
What is the ureteric bud?
An outpocketing of the distal mesonephric duct which will form the collecting system for the metanephric kidney (intermediate mesoderm)
-> induces metanephric mesenchyme to form the glomerulus through distal convoluted tubule
What does the mesonephric duct become? How does it relate to the ureter?
The male ductus system (i.e. vas deferens) which empties into the urethra. Part of the distal duct also forms the trigone of the bladder.
Ureteric bud drains above this trigone (forms ureters)
Ureteric bud drains above while the vas deferens drains below, but is looped over top of the ureters -> water UNDER the bridge.
What is seen with posterior urethral valves?
Wolffian duct abnormality -> diagnosed by hydronephrosis and thick-walled bladder. Most common bladder outlet obstruction in male infants
What renal problems will medullary sponge kidney cause?
Cystic dilation of collecting ducts -> collecting duct dysfunction
- > Type 1 RTA
- > increased risk of stones / UTIs
What renal mass is very common, benign, and marked by anechoicness on ultrasound?
Simple renal cysts
What is a complex renal cyst and what should be done about it?
Cysts that are septated, enhanced, or have solid components on imaging
-> should be followed up on or possibly removed due to increased risk of renal cell carcinoma
What are the periods of lung development up until age 20? What develops in each of these stages?
Lung bud = 4-6 weeks - up to segmental bronchi
Pseudoglandular period = 6-16 weeks - up to terminal bronchioles
Canalicular period = 16-26 weeks - up to alveolar ducts
Saccular / Alveolar period = 26 weeks to term - up to terminal sacs
Alveolar period = birth to 10 years - up to adult alveoli number
10-20 years - HYPERTROPHY of existing alveoli
What does the lung develop from and when can the lung lobes be actually distinguished? When is conduction system branching complete?
Develops from foregut endoderm
Lobes are distinguished by week 12 (pseudoglandular period), branching to terminal bronchioles is complete by week 16 (End of pseudoglandular period)
What important development happens in the canalicular stage and what cell is the precursor to type 1 and 2 pneumocytes?
Alveolar ducts develop which are lined by cuboidal cells, which are the precursor to Type 1 and 2
Important relationship is made as ducts because surrounded by a very prominent capillary network
When does the insult occur to cause tracheo-esophageal fistula and what are the symptoms? What is the most common type?
4th week of development (lung bud stage) -> failure of separation of esophagus and lung buds
Most common type: esophageal atresia with tracheoesophageal fistula
Symptoms: choking, coughing, and vomiting on first feeding which can inflate stomach and lead to aspirations of food into airways
What is a bronchogenic cyst and its clinical significance?
Abnormal development of primitive airway buds, cysts are attached to bronchial tree via defective airway
Clinical significance:
Poor mucosal clearance, recurrent infections / pneumonia which may require surgical removal
-> low pressure system which is easily removed (supplied by pulmonary circulation, vs a sequestration -> which btw is not connected to pulmonary tree)
What is the formula for distending pressure? What is its significance?
P = (2 T) / r
Where P is the pressure required to keep alveoli open, and T is the surface tension
Thus, small alveoli have a tendency to collapse. Surfactant gets concentrated to reduce T (surface tension) in small alveoli -> normalizes distending pressure across all alveoli.
Up to what point are alveolar macrophages supposed to clear?
They clear most of the respiratory (gas exchange) epithelium
Ciliated respiratory epithelium / terminal bronchioles still have a ciliary elevator which clears debris from the small airways
What gives rise to the spleen and what holds it off the posterior body wall to keep it peritoneal?
It is formed by mesenchymal cells located between the two mesothelial layers of the dorsal mesogastrium (mesoderm derived).
It is held off the posterior abdominal wall by the splenorenal ligament, and attached to the stomach by the gastrosplenic ligament.
What forms the primary intestinal loop, and what is at its center dorsally and ventrally?
Rapidly growing midgut
Dorsally: centered around superior mesenteric artery + mesentery off posterior abdominal wall (SMA goes directly in axis with vitelline duct)
Ventrally: Vitelline duct which extends to the yolk sac, located in the extraembryonic cavity of the umbilical cord on anterior abdominal wall
What causes the first rotation of the intestinal loop and what is this turn about its axis around the vitelline duct?
Causes by rapid growth of portion of midgut between distal half of duodenum and vitelline duct (the anterior half of the loop)
It rotates 180 degrees counterclockwise about its front axis, making the cecal bud and transverse colon ventral to the developing duodenum.
What happens in the final 90 degrees of rotation for the intestinal loop?
From the accelerated growth of jejunum and ileum, it rotates to a total of 270 degrees so the cecal bud lies to the right side underneath the developing liver.
How does omphalocele occur and is its prognosis better or worse than gastroschisis?
Ompalocele - failure of physiologic hernation (which occurs during growth rotation of gut during development) to return from umbilical cord back into abdomen. Will be covered by peritoneum and amnion.
Prognosis is worse than gastroschisis even though it looks less ugly, because more genetic abnormalities are associated with it
What is gastroschisis? Where does it typically happen?
Extrusion of abdominal contents through abdominal wall, not covered by peritoneum or amnion -> typically due to an abdominal wall defect on the right side
Can be repaired surgically
What is the most common place for intestinal atresia to occur and what is thought to cause it?
Duodenum - failure to recanalize due to loss of blood supply during development
Associated with Down syndrome
Who tends to get hypertrophic pyloric stenosis, and what are the common presenting signs and symptoms?
Firstborn Caucasian males
- Olive-shaped mass in epigastric region
- Visible peristaltic waves after eating (hypertrophy)
- Nonbilious projecting vomiting starting after feedings about 3-4 weeks after birth (takes a while for food to build in stomach)
Hypokalemic hypochloremic metabolic alkalosis secondary to vomiting (similar to Bulimia)
What is the hepatic diverticulum? What side does it originally start?
Bud which gives rise to liver, hepatic / bile system, gall bladder + cystic duct, and ventral pancreatic bud. It forms off of mid-duodenum
Starts on ventral side of duodenum before clockwise stomach rotation allows bile duct on the inferior right side of the duodenum
What forms the parenchymal cells of the liver and how?
Endodermal foregut gives rise to liver bud (hepatic diverticulum) around 4 weeks.
Endoderm of diverticulum grows into the mesoderm-derived mesenchyme of the septum transversum
Endoderm forms the biliary tree as well as the parenchymal cells of the liver
What will the mesenchyme of the septum transversum become?
Forms the connective tissue of the liver -> fibroblasts and stellate cells, as well as Kupffer cells and **hematopoietic stem cells in fetal liver
What forms the endothelial cells of the liver sinusoids?
Remnants of the yolk sac circulation -> vitelline and umbilical vessels
What separates the right from the left lobe of the liver? What does it contain?
The falciform ligament
Contains the round ligament (ligamentum teres) -> remnant of umbilical vein
What are the boundaries of the quadrate and caudate lobes?
Caudate - IVC laterally, porta hepatis anteriorly, ligamentum venosum medially
Quadrate - Gall bladder laterally, porta hepatis posteriorly, ligamentum teres medially
-> QUADrate is the best so its anterior -> scopes down the hallway and hits a quaaaaaaaaaaaaaadd
What does the ventral pancreatic bud give rise to?
Off of the hepatic diverticulum within the confines of the ventral mesoduodenum, it gives rise to main pancreatic duct, uncinate process, and dorsal half of head of the pancreas.
What bud forms in the dorsal mesoduodenum and what does it give rise to?
The dorsal pancreatic bud. Gives rise to ventral half of pancreatic head, the body and tail of pancreas, and the accessory pancreatic duct.
What happens to the two pancreas segments on rotation?
They both become positioned on the medial surface of the duodenum, where they fuse and the accessory pancreatic duct degenerates. It only remains functional in about 10% of people.
What occurs if the ventral pancreatic bud doesn’t know how to rotate in embryonic development?
Annular pancreas - It will rotate in both directions, around the duodenum
Risk is duodenal obstruction
What is pancreas divisum and what is the risk?
Incomplete fusion of the dorsal and ventral pancreatic buds, including incomplete ductal fusion
- > since accessory duct of dorsal bud will be smaller than main duct, some secretions will be trapped in body of pancreas
- > risk of recurrent, chronic pancreatitis
What gives rise to the parafollicular (C cells) of the parathyroid?
Neural crest -> makes sense because they are neuroendocrine in origin
Where do the endocardial tubes develop from (germ layer)?
Cardiogenic mesoderm, which forms a horseshoe cranial to buccopharyngeal membrane.
Horseshoe of mesodermal lies within splanchnic layer of lateral mesoderm of embryonic disk
What forms the pericardial cavity?
Intraembryonic coelom. As the lateral mesoderm separates, the somatic layer will surround the foregut and pericardium, and the space where the gut and heart resides comes from this coelom. -> same cavity as the peritoneal cavity until it is walled off by septum transversum
How is the inflow tract of the heart made? What vessels contribute?
Sinus venosus - receives blood from three vessels:
- Common cardinal - via systemic circulation (anterior and posterior cardial veins)
- Vitelline - i.e. portal vein
- Umbilical - via ductus venosus
What are the arms of the inverted Y of the heart tube? Central part? Top part?
The precursors of the atrial chambers (sinus venosus)
Central part is the primitive ventricle, which will mostly be the left ventricle
Top part = conotruncal segment, also known as the primitive RV + truncus arteriosus
When the heat begins folding, how do the conotruncus and AV canals shift?
Conotruncus -> shifts leftward to be more in the center of the heart
AV canal -> shifts rightward so that when the endocardial cushions are placed, the ventricles are evenly divided
This is all with respect to the primitive ventricle bending to the right and the sinus venosus shifting upward and to with left
What are the truncoconal cushions?
The neural crest derived cells which rotate to form the aorticopulmonary septum (infundibular septum) within the conotruncal segument
How are the right and left AV canals formed?
When the AV cushions form on the ventral and dorsal surfaces of the large AV canal, this separates the right ventricle from the left ventricle
What do the small endocardial cushions forming of the lateral walls of the AV canal form?
Form the mitral and tricuspid valves
(thus, membranous portion of IV septum, atrial septum, and mitral/triscupid valves are derived from endocardial cushions, which are derived from cardiac jelly)
What does the bulbus cordis become?
It is the structure that feeds into the truncus arteriosus, and will be the smooth parts of the outflow tract of the left and right ventricle
What is the sinus venarum? How does it relate to crista / sulcus terminalis?
The smooth-walled portion of the right atrium to the left of crista terminalis, which is formed by the incorporated sinus venosus
What does the original embryonic right atrium become?
The pectinate auricular appendage, to the right of crista terminalis. Contains the pectinate muscles
What does the primitive pulmonary vein become? What does the embryonic left atrium become?
Pulmonary vein - becomes smooth-walled part of definitive left atrium
Embryonic left atrium - auricular appendage which is rough
What happens to the single A-V canal?
The endocardial cushions made from cardiac jelly form on the dorsal and ventral walls, approaching one another, and fuse to make the single canal into a left and right A-V canal
What is the interventricular foramen?
This foramen is left between the two ventricles as the muscular interventricular septum results as the ventricles dilate / grow. It will eventually be fused when the AV cushions grow the membranous portion of the IV septum to seal it off.
What forms the trabeculated left ventricle?
Primitive ventricle
What do the left and right anterior cardinal veins become?
They anastomose, the left ACV below the anastomosis disappears. Superior to their anastomosis they are right and left brachiocephalic veins, inferior to the right (right common cardinal vein) becomes the superior vena cava.
What forms the IVC between the liver and the sinus venosus?
the right vitelline vein
What happens to the posterior cardinal veins?
They largely disappear - the terminal portion of the right posterior cardinal vein will persist as the azygos vein which enters the superior vena cava
What is the function of the cardiac jelly?
Separates the heart tube from the developing myocardium, and acts as structural support.
What is foramen primum?
The space left between septum primum and the AV cushions as it grows towards the AV cushions from the roof of the atrium
What is foramen secundum and when does it form?
The perforations which coalesce into a hole in the septum primum before it completely obliterates foramen primum by attaching to the endocardial cushion
What does foramen ovale become when it’s closed?
Fossa ovalis
